1. Field of the Invention
This invention relates to an improved perfusion cannula having a blood pressure sensing arrangement for use in conjunction with cardiopulmonary bypass procedures.
2. Prior Art
The field of cardiac surgery is usually defined as that specialty in the discipline of surgery that involves the operative correction of defects of the human heart. Although some early cardiac surgical operations were performed on the beating heart, the true explosion of the specialty followed the introduction by Gibbon of the pump-oxygenator in 1953. In fact, one could make the case that the field of cardiac surgery for the surgeon is defined by the use of cardiopulmonary bypass with a pump-oxygenator. With the use of this device the entire function of the patient's heart and lungs can be temporarily replaced by a machine, which allows the cardiac surgeon to operate on or in the quiet heart. This advance allowed the operative correction of many diseases that were previously untreatable, and also allowed new, more exact correction of other diseases that had only been partially approachable in the beating heart.
The performance of effective cardiopulmonary bypass requires a cannula (or cannulae) to be placed into the right side of the heart or major veins to drain blood from the patient into the pump-oxygenator. In the pump-oxygenator the blood is then exposed to a gaseous mixture (similar to the function provided by the normal lungs) that eliminates carbon dioxide and adds oxygen to the blood. The oxygenated blood is then usually passed through a heat exchange mechanism that allows the temperature of the blood to be controlled. The oxygenated blood, now cooled or warmed to the desired temperature, is returned to the body through a perfusion cannula. In the early days of cardiac surgery, and in some unusual circumstances today, that cannula is placed into a large peripheral artery, such as the common femoral artery. However, because of a higher incidence of complications associated with that method of blood return to the body, in virtually all cardiac operations today the blood is returned through a cannula placed into the ascending aorta, usually just proximal to the origin of the innominate artery.
The aortic perfusion cannula, which is returning oxygenated blood from the pump-oxygenator, is usually a piece of tapered plastic tubing. The cannula has a small bend in its distal end to direct flow into the lumen of the aorta, even though the cannula itself enters the aorta perpendicularly. The inlet end of the cannula may contain an adapter that allows the cannula to be connected directly to the plastic tubing from the pump-oxygenator that is carrying the blood back to the body.
The insertion of the aortic cannula is usually performed in the following fashion. After the patient's chest has been opened and the pericardium (sac around the heart) has been entered, concentric purse-string sutures are placed into the anterior wall of the ascending aorta just proximal to the origin of the innominate artery. The clear area in the center of the purse-string sutures is made large enough to accommodate the size of the aortic perfusion cannula. A small incision is then made through the wall of the aorta into its lumen in the center of the purse-string sutures. The aortic perfusion cannula is then inserted through that incision into the aorta, clamping the perfusion cannula so that blood will not come out of the aorta. Air is evacuated from the perfusion cannula as it is joined by a connector to the tubing from the pump-oxygenator, so that the entire system is free of any air bubbles. The purse-string sutures are then tightened to prevent the escape of blood from the aorta around the perfusion cannula.
Similar venous drainage cannulae are inserted through purse-string sutures into the right atrium of the heart or directly into the superior and inferior vena cavae for connection to the drainage side of the pump-oxygenator. Cardiopulmonary bypass is instituted by removing the clamps from the venous drainage cannulae, allowing unoxygenated blood which is returning to he right side of the heart to be diverted into the pump-oxygenator. There carbon dioxide is eliminated from the blood, oxygen is added and the temperature of the fluid is adjusted. The oxygenated blood is then pumped into the arterial return side of the pump-oxygenator, through the aortic perfusion cannula, into the patient.
During such a cardiopulmonary bypass procedure, the blood pressure of the patient must be monitored. Monitoring is most often carried out through a small catheter inserted percutaneously into a small peripheral artery, usually the radial artery of the wrist. Unfortunately, measurement of the arterial pressure through a radial cannula is not always accurately reflective of the central aortic pressure because of local resistance changes that can be caused by temperature or pharmacologic agents used during cardiopulmonary bypass procedures. This is a serious drawback to the efficiency and effectiveness of cardiopulmonary bypass procedures in general, since it is vitally important that blood pressure be maintained within a certain acceptable range. When blood pressure is below the acceptable range, perfusion of the organs of the body can be seriously compromised, leading to significant damage; and when the pressure exceeds acceptable limits excessive bleeding and possible organ damage can result. Mismeasurement can also be caused by peripheral arterial vascular disease. Consequently, the present inventor sought an improved arrangement for use with cardiopulmonary bypass procedures. Careful and extensive research led to the discovery of the invention described hereinbelow.